Although low-grade parasite persistence is a fundamental aspect of chronic Chagas disease, current parasitological assays have low sensitivity and are not quantitative. Benznidazole, the only available trypanocidal drug, has questionable efficacy in the treatment of chronic Chagas disease patients. There is an urgent need to perform clinical trials of new drugs for chronic Chagas disease, however the lack of reliable biomarkers for reduction of parasitism and consequent inflammatory responses and damage is a major obstacle for evaluating new drugs. The identification of differentiating markers for presence and levels of 7. crtvz; parasitism and resulting immune and inflammatory perturbations could potentially solve this problem. The few available biomarkers for parasitism and disease progression are neither quantitative nor highly predictive. It is known that composite biomarkers have a higher potential for differentiating clinical outcomes than single markers. Blood gene expression profiling has been used to differentiate between patients with distinct courses of infection in several infectious diseases including preliminary data from our group for Chagas disease. We hypothesize that persistent parasitism by 7. cruzi, induces specific changes in PBMC gene expression patterns. A second hypothesis is that distinct stages of infection, defined based on clinical presentation and findings and 7. cruzi PCR and antibody results, will display specific composite biomarker profiles. The major aims of this project are to identify the transcriptional profiles of high and low 7. cruzi parasitism as well as the transcriptional profiles of patients with different clinical presentations, and to combine the findings from transcriptome analyses with other biomarker parameters we are currently characterizing. The study will evaluate a sample of patients representative of distinct clinical stages of Chagas disease and intensity of parasitism (as measured by 7. cruzi real-time PCR), along with seronegative controls, from the REDS II Chagas cohort. Transcriptome analysis of whole blood will be performed, and transcriptional signatures that correlate with each clinical group will be validated with qPCR assays that can be applied to larger sample sets. We will then test the classifying ability of validated mRNA markers on the remainder of the REDS II Chagas disease cohort (600 patients and 100 seronegative controls). Plasma protein biomarkers of inflammation and cardiovascular disease and 7. cruz/antibody profiles/titers, which are being characterized in the same patient groups, will be combined with transcriptome signatures to construct an improved composite biomarker profile for prognosis and therapeutic monitoring.